Protectors for electric circuits



Jan. 4, A. J. GAIA PROTECTORS FOR ELECTRIC CIRCUITS Filed Sept. 19, 1960 INVENTOR. ALB/N0 J. GA/A United States Patent C) 3,227,841 PR'UTECTQRS FQR ELECTRKC CIRCUITS Aldino .l'. Gaia, St. Louis, Mo., assignor to McGraw- Edison Company, Eight, lit, a corporation of Delaware Filed Sept. 19, 1960, Ser. No. 56,884 4 Claims. (Cl. 260-413) This invention relates to improvements in protectors for electric circuits. More particularly, this invention relates to improvements in miniature small enclosed electric fuses.

It is therefore an object of the present invention to provide an improved small enclosed electric fuse.

There is a progressive demand for reductions in the sizes of electrical components; and that demand has been extended to the art of electric fuses. However it is not always easy to reduce the sizes of electric fuses, because an electric fuse must have an arc gap that is large enough to clear any arcs that form as the fuse opens the circuit. Yet, it would be desirable to provide extremely small enclosed electric fuses. The present invention provides such fuses; and it is therefore an object of the present invention to provide an extremely small enclosed electric fuse.

The fuse provided by the present invention can be small enough to fit within a housing that is approximately one quarter of an inch long and approximately one quarter of an inch in diameter; and yet that fuse can be used to open circuits carrying two hundred and forty volts. The present invention attains this startling result by connecting the fusible conductor of the fuse to terminals that are circular in cross section and that are disposed immediately adjacent the inner surface of the housing and by making the wall of that housing thin. Those terminals serve as fixed arc horns which are spaced apart a distance greater than one half the inner diameter of the housing. Further, those terminals are massive relative to the fusible conductor and will thus cool any are that forms as the fusible conductor opens the circuit. In addition, the fusible conductor extends transversely of the axes of those terminals so the convex surfaces of those terminals can simulate spherical arc horns and thereby facilitate the quenching of any arc that forms as the fusible conductor opens the circuit. It is therefore an object of the present invention to provide an electric fuse which has its fusible conductor connected to, and extending transversely of the axes of, terminals which are circular in cross section and which are disposed immediately adjacent the inner surface of a thin-walled housing.

It is usually desirable to provide a way of readily determining whether the fusible conductor of a fuse is intact or has fused to open the circuit; but with an extremely small enclosed electric fuse it is particualrly desirable to provide a way of readily determining whether the fusible conductor of that fuse is intact or has fused to open the circuit. Such a fuse could not be tested by an ohmmeter, because the current supplied by the battery of the ohmmeter could cause the fusible conductor to fuse. While that fuse could he removed and a substitute fuse could be inserted in its place, such removal and insertion is time-consuming and would subject the fuse to needless stresses and strains. Further, it would be difficult to know whether the fusible conductor of the substitute fuse was intact. Hence, it would be extremely desirable to provide a way of readily determining whether the fusible conductor of an extremely small enclosed electric fuse is intact or has fused to open the circuit. Yet the extremely small size of such a fuse makes it impossible to equip that fuse with a window of the usual type. The present invention provides a way of readily determining whether the fusible conductor of an extremely small enclosed electric fuse is intact or has fused to open the circuit, and it does so by providing a window for that fuse. It

is therefore an object of the present invention to provide an extremely small enclosed electric fuse with a window.

Where a fuse must fit within a housing that is approximately one quarter of an inch long and approximately one quarter of an inch in diameter, the components of that fuse must be extremely small. Such small components are hard to handle; and it would be desirable to pro vide a way of facilitating the handling of such small components. The present invention provides a Way of facilitating the handling of the small components of the fuse of the present invention. Specifically, the present invention provides a relatively large mounting, secures the fuse terminals to that mounting, and then secures the fusible conductor to those terminals. That mounting, those terminals and that fusible conductor constitute a readilyhandled and relatively rugged sub-assembly. It is therefore an object of the present invention to provide a relatively large mounting to which the fuse terminals can be secured, and which coacts with said fuse terminals and with a fusible conductor to constitute a readily-handled and relatively rugged sub-assembly.

The housing of the fuse provided by the present invention has a thin wall, and a portion of that wall is rendered even thinner to define a shoulder. That shoulder is frustoconical in configuration; and it performs the dual func tions of limiting the extent to which the mounting can be telescoped into the housing and of centering that mount ing relative to that housing. It is therefore an object of the present invention to further reduce the thin Wall of the housing of a fuse to form a frusto-conical shoulder that can limit the extent to which the mounting can be telescoped into the housing and that can center that mounting relative to that housing.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description a preferred embodiment of the present invention is shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing, FIG. 1 is a plan view of one form of small enclosed electric fuse that is made in accordance with the principles and teachings of the present invention,

FIG. 2 is a sectional view through the fuse of FIG. 1, and it is taken along the plane indicated by the line 2-2 in FIG. 1,

FIG. 3 is a view of the bottom of the fuse of FIG. 1, and

FIG. 4 is a cross sectional view of the mounting, the fuse terminals and the fusible conductor of the fuse of FIG. 1.

Referring to the drawing in detail, the numeral 10 generally denotes the housing for one embodiment of small enclosed electric fuse that is made in accordance with the principles and teachings of the present invention. That housing is made of insulating material, and it is preferably made of a refractory material; because such material can be strong and can have a high dielectric value. One such material is steatite. The housing MD is hollow, as at 16, and it is cylindrical; and that housing has an inwardlyextending annular flange 1.4 at the upper end thereof. That flange defines a circular opening 12 at the upper end of the housing; and the diameter of that opening is smaller than the inner diameter of the housing It). The lower end of the housing 10 is formed so it is initially completely open. The wall of the housing 10 is made thin so the hollow center 16 of that housing has a large diameter. The lower portion of the wall of the housing 10 is made even thinner to provide a reduced-thickness portion 18. That reduced-thickness portion coacts with the full thickness portion of the wall of housing to define a shoulder which is frusto-conical in configuration. The angle of generation of that shoulder is preferably between forty-five and seventy degrees.

The numeral 22 denotes a disc of transparent material; and one suitable transparent material is self-extinguishing cellulose acetate. That material is commercially available, and it is sold under the mark Plastacele. The diameter of the disc 22 is larger than the diameter of the opening 12 at the upper end of the housing 10, but that diameter is small enough to permit that disc to be telescoped within the housing 10. The diameter of the disc 22 is preferably large enough to enable that disc to have a press fit with the full thickness portion of the wall of the housing 10. As a result, when the disc 22 is pressed into position where it abuts the under face of the flange 14, that disc will resist movement relative to the housing 10. That disc will serve as a window for the housing It). The annular flange 14 will abut, and will overlie, the outer portions of the upper face of the disc 22; and it will thereby prevent the expulsion of that disc through the upper end of the housing It). That flange will thus coact with the press fit between the disc 22 and the inner surface of the full thickness portion of the wall of the housing 10 to fixedly lock that disc in position within the housing 10.

The numeral 24 denotes a mounting, in the form of a disc, which has a diameter that is just slightly smaller than the inner diameter of the reduced-thickness portion 18 of the wall of the housing 10. That mounting is electrically non-conductive, and it is preferably made of a refractory material; because such a material can be strong and can have a high dielectric value. One such material is steatite. The mounting 24 has a pair of openings 26 therein, and those openings are parallel to the geometric axis of that mounting. Those openings are located on a diameter of the mounting 24, and they are adjacent the periphery of that mounting. However, the openings 26 are spaced inwardly a short distance from the periphery of the mounting 24, so that the outermost portions of those openings will be spaced just a short distance in wardly of the horizontal projection of the full thickness portion of the wall of the housing it) whenever the mounting is telescoped within that housing.

The openings 26 in the disc 24 accommodate terminals 28; and those terminals are electrically conductive and are circular in cross section. Those terminals are suitably fixed in position within the openings 26 by being crimped, upset or staked, by being cemented to the mounting 24, or by any other suitable artifice. As indicated by FIG. 4, the terminals 28 are initially parts of a length of wire which has been bent to have a U-shaped configuration. After that wire has been given its U-shaped configuration,

the free ends thereof are telescoped into and through the openings 26 in the mounting 24. Those free ends of that wire extend upwardly above the upper face of the mounting 24 distances approximating the vertical length of the shoulder 20 at the interior of the housing 10. While the terminals 28 are still part of the U-shaped wire, those terminals are fixedly secured within the openings 26.

A small diameter fusible conductor 30 is secured to the upper ends of the terminals 28 by masses 31 of solder. That solder is high temperature solder, and it will not melt during normal operation of the fuse. The masses 31 of solder provide full electrical connection between the fusible conductor 30 and the terminals 28, and they hold that conductor fixed relative to the mounting 24. It will be noted that the fusible conductor 30 extends transversely of the axes of the terminals 28.

The engagement between the terminals 28 and the mounting 24 and the engagement between the fusible conductor 30 and the terminals 28 are such that the mounting 24 and the terminals 28 and the fusible conductor 30 constitute a sub-assembly. That sub-assembly is readily handled and is relatively rugged. Further, the closed end of the U-shaped wire, of which the terminals 28 are a part, constitutes a convenient handle or fingerreceiving member. The overall result is that the said subassembly is easily handled despite its very small size.

The mounting 24- can be assembled with the housing 10 by moving that mounting toward that housing to telescope the fusible conductor 30? and the upper ends of the terminals 28 through the open lower end of the housing 1t and by continuing to move that mounting toward that housing until the periphery of that mounting engages and is held by the shoulder 26 at the interior of the housing 10. As the mounting 24 engages the shoulder 20, that shoulder will precisely center that mounting relative to the housing It]. As a result, the shoulder 243 performs the dual functions of limiting the extent to which the mounting 24 can be moved toward the disc 22 and of precisely centering that mounting within the housing 10. At the time the mounting 24 is centered, the terminals 255 will be spaced inwardly from, and thus not in contact with, the housing 10; and this is desirable. Also, at the time the mounting 24 is in position, the bottom face of the mounting will be disposed a short distance above the level of the bottom of the housing 10.

Once the mounting 24 has been set in position, a sealing material 32 such as an epoxy resin is placed in engagement with the under surface of that mounting. At the time that sealing material is placed in engagement with that under surface of mounting 24, the housing 10 and the mounting 24 will be inverted, from the position shown by FIG. 2, so that gravity will urge that sealing material against that mounting. The sealing material 32 will also engage and bond to the terminals 28 and to the reducedthickness portion 18 of the wall of the housing 10. The sealing material 32 will not be able to flow into the interior of the housing 10 because the mounting 24 will coact with the shoulder 20 to prevent any inflow of that sealing material.

It will be noted that the spacing between the terminals 28 is greater than one half the diameter of the interior 16 of the housing It). As a result, the present invention provides a large arc gap between the terminals 28. Further it will be noted that the cross sections of the terminals 28 are very much larger than the cross section of the fusible conductor. In one preferred embodiment of the present invention, the diameter of each terminal 28 is four hundredths of an inch, and hence the cross sectional area of each terminal is approximately thirteen ten thousandths square inch. The diameter of the fusible conductor 30 can range from as large as five thousandths of an inch to as small as one ten thousandths of an inch or smaller. As a result, the cross sectional area of that fusible conductor can range from as large as nineteen millionths of a square inch to as small as eight billionths of a square inch or smaller. This means that while the terminals 28 are small, they are very massive relative to the fusible conductor 30 and will cool any are that forms when the fusible conductor 30 opens the circuit. In addition, it will be noted that as an arc would tend to span the gap between the terminals 28, that are would be intermediate two convex surfaces; and those surfaces would simulate spherical arc horns. These various features coact to enable this extremely small fuse to safely open circuits which are carrying two hundred and forty volts.

After the sealing material 32 has set and hardened, the closed end of the wire, of which the terminals 28 are a part, is cut oif. The dashed line AA in FIG. 4 shows where that closed end will be cut away. The cutting away of that closed end forms two prongs, as shown by FIGS. 2 and 3. Those prongs can extend into a suitable socket to connect the fuse into the circuit which it is to protect.

To be effective in cooling any are that forms as the fusible conductor 30 opens the circuit, the terminals 28 should have cross sections that are very much larger than the cross section of that fusible conductor. Specifically, those terminals should have cross sections that are approximately one hundred or more times the cross section of that fusible conductor.

It will be noted that the upper ends of the terminals 28 are not only spaced apart but are spaced from nearby surfaces. As a result, those upper ends will facilitate the heat-induced upward bowing of any arc that forms between those upper ends; and such upward bowing will help tend to quench the arc.

Whereas the drawing and accompanying description have shown and described a preferred embodiment of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention Without affecting the scope thereof.

What I claim is:

1. An enclosed electric fuse that comprises a hollow cylindrical housing, an inwardly-directed annular flange adjacent one end of said housing, said inwardly-directed annular flange defining an opening at said one end of said housing which has a diameter that is smaller than the inner diameter of said housing, a disc of transparent material telescoped within said housing, said disc abutting the inner face of said inwardly-directed annular flange and constituting a window, said inwardly-directed annular flange overlying the outer portions of the outer face of said disc and thereby preventing expulsion of said disc through said one end of said housing, the periphery of said disc snugly engaging the interior of said housing to hold itself against movement relative to said housing, a second disc, said second disc being electrically non-conductive, said second disc being telescoped within said housing, an opening in said second disc adjacent to but spaced inwardly from the periphery of said second disc, an electrically conductive terminal disposed within said opening in said second disc and projecting above and below the upper and lower faces of said second disc, at second opening in said second disc adjacent to but spaced inwardly from the periphery of said second disc, said openings in said second disc being on a diameter of said disc, a second electrically conductive terminal disposed within said second opening in said second disc and projecting above and below the upper and lower faces of said second disc, said terminals being fixedly secured to said second disc and having the upper ends thereof spaced the same distances from said upper face of said second disc, said terminals having the lower ends thereof spaced the same distances from said lower face of said second disc, a fusible conductor that is electrically connected to said upper ends of said terminals by solder, said fusible conductor being disposed below the level of but being visible through said disc of transparent material, the lower ends of said terminals serving as prongs that can extend into a socket to connect said fusible conductor into a circuit, and an insulating material that engages said second disc and said housing and that bonds said second disc to said housing, said terminals being adjacent but spaced inwardly from the interior of said housing whenever said second disc is telescoped within said housing, said upper ends of said terminals constituting fixed arc horns that are spaced apart a distance greater than one half the inner diameter of said housing, whereby any are that forms as said fusible conductor opens the circuit will clear, said terminals being massive relative to said fusible conductor to cool any are that forms as said fusible conductor opens the circuit, said terminals being circular in cross section and said fusible conductor extending transversely of the axes of said terminals, whereby said terminals serve as spherical arc horns, said terminals being parallel to the axis of said housing whenever said second disc is disposed within said housing, said housing having a thin wall and having a portion of that wall of even less thickness to define an annular shoulder at the interior of said housing said shoulder being frusto conical in configuration, said shoulder limiting the extent to which said second disc 6 can be telescoped within said housing, said shoulder centering said second disc as said second disc is telescoped within said housing, said housing and said disc of transparent material and said second disc constituting a unitary enclosure for said fusible conductor.

2. An enclosed electric fuse that comprises a hollow cylindrical housing, a thick-walled portion for said housing, a thin-walled portion for said housing, a shoulder defined by an intermediate said portions, a mounting, said mounting being electrically non-conductive, said mounting having an area smaller than the area defined by said thin-walled portion and said mounting being telescoped within said housing, said mounting having an area larger than the area defined by said thick-walled portion whereby said mounting engages and is held by said shoulder, said shoulder being tapered, terminals supported on and carried by said mounting, a fusible conductor soldered to and carried by said terminals, said shoulder limiting the extent to which said mounting is telescoped within said housing and acting to automatically center said mounting Within said housing as said mounting is telescoped within said housing and is moved into abutting engagement with said shoulder, and a sealant that underlies said mounting and that engages said mounting and said housing and said terminals, said sealant constituting substantially the sole means of holding said mounting in assembled relation with said housing.

3. An enclosed electric fuse that comprises a hollow housing that has a closed top which substantially prevents the escape of arcing products, a mounting, said mounting being electrically non-conductive, said mounting being telescoped Within said housing, an opening in said mounting, an electrically conductive terminal snugly disposed within and substantially filling said opening in said mounting, a second opening in said mounting, a second electrically conductive terminal snugly disposed within and substantially filling said second opening in said mounting, a sealant that fixedly secures said terminals to said mounting and that substantially prevents the escape of arcing products, and a fusible conductor that is electrically connected to said upper ends of said terminals by solder, said upper ends of said terminals constituting fixed arc horns that are spaced apart a distance greater than one half the inner diameter of said housing and being spaced a substantial distance away from the closed top of said housing, whereby any are that forms as said fusible con-- ductor opens the circuit will clear, said terminals being massive relative to said fusible conductor to cool any are that forms as said fusible conductor opens the circuit, said terminals being circular in cross section, and said fusible conductor extending transversely of the axes of said terminals, whereby said terminals serve as spherical arc horns.

4. An enclosed protector for electric circuits that comprises a hollow housing, a pair of terminals that extend into said housing, and a fusible conductor that is soldered to and that extends between said terminals, said terminals being circular in cross section, said terminals being spaced apart to provide an arc gap, said terminals having cross sections that are approximately one hundred or more times the cross section of said fusible conductor.

References Cited by the Examiner UNITED STATES PATENTS 930,675 8/1909 Menzel 200129 1,681,239 8/1928 Johnson et al 200-130 1,957,480 5/1934 Van Emden 200- 2,059,681 11/1936 Crimmins 200- 2,412,712 12/1946 Brown 29155.5 2,734,110 2/1956 Jacobs 200120 2,740,187 4/1956 Jacobs et al. 29155.5

(Other references on following page) UNITED STATES PATENTS FOREIGN PATENTS France. Germany.

Great Britain. Great Britain. Great Britain.

8 OTHER REFERENCES De Backer: Terminal Bases for Vacuum Tubes, RCA Technical Notes, RCA Laboratories, Princeton, NJ. RCA TN. #75 Dec. 2, 1957, 1 page only.

BERNARD A. GILHEANY, Primary Examiner.

RICHARD M. WOOD, ROBERT K. SCHAEFER,

Examiners. 

1. AN ENCLOSED ELECTRIC FUSE THAT COMPRISES A HOLLOW CYLINDRICAL HOUSING, AN INWARDLY-DIRECTED ANNULAR FLANGE ADJACENT ONE END OF SAID HOUSING, SAID INWARDLY-DIRECTED ANNULAR FLANGE DEFINING AN OPENING AT SAID ONE END OF SAID HOUSING WHICH HAS A DIAMETER THAT IS SMALLER THAN THE INNER DIAMETER OF SAID HOUSING, A DISC OF TRANSPARENT MATERIAL TELESCOPED WITHIN SAID HOUSING, SAID DISC ABUTTING THE INNER FACE OF SAID INWARDLY-DIRECTED ANNULAR FLANGE AND CONSTITUTING A WINDOW, SAID INWARDLY-DIRECTED ANNULAR FLANGE OVERLYING THE OUTER PORTIONS OF THE OUTER FACE OF SAID DISC AND THEREBY PREVENTING EXPULSION OF SAID DISC THROUGH SAID ONE END OF SAID HOUSING, THE PERIPHERY OF SAID DISC SNUGLY ENGAGING THE INTERIOR OF SAID HOUSING TO HOLD ITSELF AGAINST MOVEMENT RELATIVE TO SAID HOUSING, A SECOND DISC, SAID SECOND DISC BEING ELECTRICALLY NON-CONDUCTIVE, SAID SECOND DISC BEING TELESCOPED WITHIN SAID HOUSING, AN OPENING IN SAID SECOND DISC ADJACENT TO BUT SPACED INWARDLY FROM THE PERIPHERY OF SAID SECOND DISC, AN ELECTRICALLY CONDUCTIVE TERMINAL DISPOSED WITHIN SAID OPENING IN SAID SECOND DISC AND PROJECTING ABOVE AND BELOW THE UPPER AND LOWER FACES OF SAID SECOND DISC, A SECOND OPENING IN SAID SECOND DISC ADJACENT TO BUT SPACED INWARDLY FROM THE PERIPHERY OF SAID SECOND DISC, SAID OPENINGS IN SAID SECOND DISC BEING ON A DIAMETER OF SAID DISC, A SECOND ELECTRICALLY CONDUCTIVE TERMINAL DISPOSED WITHIN SAID SECOND OPENING IN SAID SECOND DISC AND PROJECTING ABOVE AND BELOW THE UPPER AND LOWER FACES OF SAID SECOND DISC, SAID TERMINALS BEING FIXEDLY SECURED TO SAID SECOND DISC AND HAVING THE UPPER ENDS THEREOF SPACED THE SAME DISTANCES FROM SAID UPPER FACE OF SAID SECOND DISC, SAID TERMINALS HAVING THE LOWER ENDS THEREOF SPACED THE SAME DISTANCES FROM SAID LOWER FACE OF SAID SECOND DISC, A FUSIBLE CONDUCTOR THAT IS ELECTRICALLY CONNECTED TO SAID UPPER ENDS OF SAID TERMINALS BY SOLDER, SAID FUSIBLE CONDUCTOR BEING DISPOSED BELOW THE LEVEL OF BUT BEING VISIBLE THROUGH SAID DISC OF TRANSPARENT MATERIAL, THE LOWER ENDS OF SAID TERMINALS SERVING AS PRONGS THAT CAN EXTEND INTO A SOCKET TO CONNECT SAID FUSIBLE CONDUCTOR INTO A CIRCUIT, AND AN INSULATING MATERIAL THAT ENGAGES SAID SECOND DISC AND SAID HOUSING AND THAT BONDS SAID SECOND DISC TO SAID HOUSING, SAID TERMINALS BEING ADJACENT BUT SPACED INWARDLY FROM THE INTERIOR OF SAID HOUSING WHENEVER SAID SECOND DISC IS TELESCOPED WITHIN SAID HOUSING, SAID UPPER ENDS OF SAID TERMINALS CONSTITUTING FIXED ARC HORNS THAT ARE SPACED APART A DISTANCE GREATER THAN ONE HALF THE INNER DIAMETER OF SAID HOUSING, WHEREBY ANY ARC THAT FORMS AS SAID FUSIBLE CONDUCTOR OPENS THE CIRCUIT WILL CLEAR, SAID TERMINALS BEING MASSIVE RELATIVE TO SAID FUSIBLE CONDUCTOR TO COOL ANY ARC THAT FORMS AS SAID FUSIBLE CONDUCTOR OPENS THE CIRCUIT, SAID TERMINALS BEING CIRCULAR IN CROSS SECTION AND SAID FUSIBLE CONDUCTOR EXTENDING TRANSVERSELY OF THE AXES OF SAID TERMINALS, WHEREBY SAID TERMINALS SERVE AS "SPHERICAL" ARC HORNS, SAID TERMINALS BEING PARALLEL TO THE AXIS OF SAID HOUSING WHENEVER SAID SECOND DISC IS DISPOSED WITHIN SAID HOUSING, SAID HOUSING HAVING A THIN WALL AND HAVING A PORTION OF THAT WALL OF EVEN LESS THICKNESS TO DEFINE AN ANNULAR SHOULDER AT THE INTERIOR OF SAID HOUSING SAID SHOULDER BEING FRUSTO CONICAL IN CONFIGURATION, SAID SHOULDER LIMITING THE EXTENT TO WHICH SAID SECOND DISC CAN BE TELESCOPED WITHIN SAID HOUSING, SAID SHOULDER CENTERING SAID SECOND DISC AS SAID SECOND DISC IS TELESCOPED WITHIN SAID HOUSING, SAID HOUSING AND SAID DISC OF TRANSPARENT MATERIAL AND SAID SECOND DISC CONSTITUTING A UNITARY ENCLOSURE FOR SAID FUSIBLE CONDUCTOR. 